13 replies to this topic

[Benzo4gT]

I have CP pistons that have been ceramic coated and dry film on the sides, Everything was machined, balanced and test fitted by Jack bros. I spoke with them about my needs, rpm limit and boost before machining and they machined a piston to bore clearance of .0035.

 

The dry film adds .0010 thickness to the mix bringing total PTB clearance of .0025. My fear is that it might be a little tight for CPs combined with high rpm and boost (9k and 30ish psi). Has anyone had any experiences with CP pistons with these coatings? I have heard that they expand a bit more than wiseco and the like.

It's not going to see any track work and will probably only see quarter mile amounts of WOT at a time, maybe a bit more depending on if I'm losing   

 

Any advice would be appreciated as I'll be building fairly soon and I don't want to balls it up due to something this simple.

[jack be nimble]

What do cp recommend?

[Benzo4gT]

I haven't gotten any info on CP's as they did not come with the sheet, but I from the info I can gather around the place it should be around .0030.

 

CP's are noted for being a bit tight on their specs considering the amount they expand hence my query regarding the dry film and whether it will help or hinder the engine.

[jack be nimble]

Email them. They are the gurus.

[jack be nimble]

The spec sheet here says 3.5 thou, as you had first machined (but it is 3yrs old spec sheet)
http://www.dsmtuners...earance.428812/
looks like you will be too tight. But i would still wait for reply from cp regards the coating and ptw.

[Benzo4gT]

I don't think I'll risk it. I'm going to send the block down to get re-done, Jack bros are going to measure each piston and allocate it a specific bore if they need to.

 

Bummer  Lesson learnt

[VIN18M]

I'm running CPs in my 93, and althought I don't remember the exact clearances (machine shop sorted it for me), I can say that my engine doesn't have the normal rattly sound of a forged motor on cold startup. Which to me would indicate tight clearances.

 

It's just a theory and not sure if I'm really adding anything here now that I think about it...

[jack be nimble]

Id still talk to cp. Are you going to get 3 or 3.5 thou?

[Benzo4gT]

I'll go for 3.5

[DOUGMO]

the dry coating is pretty much sacrificial anyway, those clearances are fine imo, I ran tighter on mine (3 thou then coated)

 

your call at the end of the day though

[bazeng]

Ditto. The film will wear out. Do not include the coating in your measurements.

I did the same with my coated piston. Deduct a thou from measurements.

You want 4 thou measure 3 thou.

Edited by bazeng, 13 May 2015 - 07:55 PM.

[Benzo4gT]

Good to hear you guys have run them in similar spec, that changes things completely. I owe you blokes a beer or two   

 

I spoke to the guy who coated them this again this morning and he mentioned that they abrasive blast the skirts to promote adhesion, so the thickness could be as little as half a thou which I am fine with.

[OLDIE]

I'm running CPs in my 93, and althought I don't remember the exact clearances (machine shop sorted it for me), I can say that my engine doesn't have the normal rattly sound of a forged motor on cold startup. Which to me would indicate tight clearances.

 

It's just a theory and not sure if I'm really adding anything here now that I think about it...

 

I would have thought that a loose fit piston would be "rattly on start up"

[BYBY5L]

Yea vin means his engine hasnt got the cold start rattle which indicates to him, he has a tight ptw gap,
my old sr20 had forgies in nz, I hated the cold start which is why I tried to stay away from forged pistons in my dailys but now with the composites used in different %s apparently its a thing of the past,